Are you looking at it with a 10-bit monitor? If not your gradient is going to band once it hits a certain size (like 256 pixels f/ full greyscale white to black). That doesn’t mean the comp is banding, it just means your display is. And everyone who looks at it on an srgb 8-bit display or worse (most lcds are 6-bit) will see it banding as well. In fact even a 10-bit display should band in certain circumstances (> 1024 pixels of full greyscale ramp).
To minimize it:
You can add grain.
You can also add an adjustment layer with the 4-color gradient, use the ‘color’ transfer mode (or any really) with a very low opacity. All of those will give your display more colors to work with to reduce banding.
Even on a 6-bit or 8-bit display, you should still work in a 16-bit or higher project as you are when addressing this issue.
Cory
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Cory Petkovsek
Corporate Video